I have in the past made IR transmission of serial data. I had many problems with the thing working correctly until I made the transmit waveform be modulated with the 16x baud rate clock. Then in the receiver end you recover this clock and use it to as the baud rate clock for the receiver UART. Then it worked great.

I also made at one time a magnetically coupled serial transmitter / receiver pair. In that application the transmit data was modulated with the 1X baud rate clock to create a data stream with a Manchester type encoding (XOR gate with clock and data). At the receiver end a magnetic pulse recovery circuit was used to re-cover the machester waveform and a small PLL was used to increase the recovered clock to 16x to feed the UART clocking on the receive side. The magnetic scheme used two coils 1.75 inches in diameter that with only 4 turns per coil. The distance supported was about 1.5 inches if the coils were parallel. It was used to send data between two pieces of medical eqipment. The pieces of equipment were designed to stack on top of one another. One coil was mounted in the rubber foot on the bottom of one cabinet. The other cabinet had depressions in its top surface to set the feet of the upper cabinet in. The other coil was placed in the bottom of the depression in a pad that was glued in there. For full duplex communication between the two cabinets two foot/depression pairs were used. It worked very reliably up to 38400 baud as I recall.

Michael Karas